太陽光エネルギー変換系のためのビスマス系オキシハライド及びカルコハライド半導体の開発

京都大学0048新制・課程博士博士(工学)甲第20582号工博第4362号新制||工||1678(附属図書館)京都大学大学院工学研究科物質エネルギー化学専攻(主査)教授 阿部 竜, 教授 陰山 洋, 教授 安部 武志学位規則第4条第1項該当Doctor of Philosophy (Engineering)Kyoto UniversityDGA

Low-Temperature Synthesis of Bismuth Chalcohalides: Candidate Photovoltaic Materials with Easily, Continuously Controllable Band gap.

光吸収の自在制御が可能な金属カルコハライドの低温合成法を開発 －フレキシブル太陽電池や発光ダイオードへの応用に期待－. 京都大学プレスリリース. 2016-09-08.Although bismuth chalcohalides, such as BiSI and BiSeI, have been recently attracting considerable attention as photovoltaic materials, the methods available to synthesize them are quite limited thus far. In this study, a novel, facile method to synthesize these chalcohalides, including BiSBr[1-x]I[x] solid solutions, at low temperatures was developed via the substitution of anions from O[2-] to S[2-] (or Se[2-]) using bismuth oxyhalide precursors. Complete phase transition was readily observed upon treatment of BiOI particles with H[2]S or H[2]Se at surprisingly low temperatures of less than 150 °C and short reaction times of less than 1 h, producing BiSI and BiSeI particles, respectively. This method was also applied for synthesizing BiSBr[1-x]I[x'] where continuous changes in their band gaps were observed depending on the ratio between iodine and bromine. The composition of all elements (except oxygen) in the chalcohalides thus produced was almost identical to that of the oxyhalide precursors, attributed to the suppressed volatilization of halogens at such low temperatures. All chalcohalides loaded on FTO clearly exhibited an anodic photocurrent in an acetonitrile solution containing I(-), attributed to their n-type nature, e.g., the BiSI electrode exhibited high IPCE (64% at 700 nm, +0. 2 V vs. Ag/AgCl)

Layered Perovskite Oxychloride Bi₄NbO₈Cl: A Stable Visible Light Responsive Photocatalyst for Water Splitting

Mixed anion compounds are expected to be a photocatalyst for visible light-induced water splitting, but the available materials have been almost limited to oxynitrides. Here, we show that an oxychrolide Bi₄NbO₈Cl, a single layer Sillen–Aurivillius perovskite, is a stable and efficient O₂-evolving photocatalyst under visible light, enabling a Z-scheme overall water splitting by coupling with a H₂-evolving photocatalyst (Rh-doped SrTiO₃). It is found that the valence band maximum of Bi₄NbO₈Cl is unusually high owing to highly dispersive O-2p orbitals (not Cl-3p orbitals), affording the narrow band gap and possibly the stability against water oxidation. This study suggests that a family of Sillen–Aurivillius perovskite oxyhalides is a promising system to allow a versatile band level tuning for establishing efficient and stable water-splitting under visible light